Conventionally, for example, in manufacturing facilities, storage facilities and receiving facilities producing liquefied gas (liquefied natural gas (LNG), liquefied petroleum gas (LPG), etc.), various gases such as raw material gas, refrigerant gas, boil-off gas, supply gas, etc. are pressurized to appropriate pressure levels from low pressure to pressure and then transferred using various pipe paths. In order to prevent device breakage due to excessive rise in gas pressure in system, such method is used of transferring the gas to a flare facility by relieving from pressure safety valves installed on to the paths, and burning the gas to discard in the flare facility (for example, refer to Patent Document 1).
In the liquefied gas storage facility described in Patent Document 1, liquefied gas stored in a liquefied gas storage tank is pumped to a vaporizer, the liquefied gas is heated by the vaporizer to be vaporized. The vaporized gas is sent to a vaporized gas supply line to a demand side gas line. A liquefied gas removal line is provided with first shut off valve, and on the downstream side of the first shut off valve a liquefied gas return line returning the liquefied gas to the liquefied gas storage tank is connected, and the liquefied gas return line is provided with second shut off valve. The vaporized gas supply line is provided in order from the upstream side with a safety valve, a demand side shut off valve, and a stack shut off valve, and a flare stack is connected to the stack shut off valve via a stack line.
In this facility, during normal operation, the first shut off valve and the demand side shut off valve are released, and the safety valve, the stack shut off valve and the second shut off valve are closed, and for example, if the demand side gas line is suffered by an abnormality, the first shut off valve and the demand side shut off valve are shut off, the pump stops, and the stack shut off valve and the second shut off valve are released. Also, releasing the safety valve prevents the equipment from being damaged due to an excessive rise in pressure in the vaporized gas supply line. Further, returning the vaporized gas to the liquefied gas storage tank via the liquefied gas return line reduces the amount of releasing the vaporized gas in the line from the safety valve and the amount of vaporized gas to be processed with the flare stack.